Regarding a bogie of a railcar, conventionally proposed is a steering bogie configured such that an angle of an axle in a yawing direction is changed along a curved track (see PTLs 1 to 4, for example). According to this, lateral force (turning resistance force) acting on wheels when the bogie passes through a curved line is reduced. Therefore, running stability of the bogie when the bogie passes through a sharp curved line improves. In addition, fricative sounds generated between the wheel and a railway track are reduced, and wear of the wheels and the like can also be reduced.
However, if a parallel cardan driving system driving bogie is provided with a steering mechanism, the axle steered when the bogie turns is largely displaced in the yawing direction, and this exceeds an allowable deviation of a WN gear coupling connecting a reducer and an electric motor. The WN gear coupling allows the deviation by a backlash formed between an internal tooth of an outer tube and an external tooth of an inner tube. However, since proper meshing between the internal tooth and the external tooth needs to be maintained, increasing the backlash has a limit. Therefore, a parallel cardan driving system driving bogie having a steering function does not exist currently.
Here, PTL 5 proposes a steering bogie configured such that: one of axles is a driving shaft; the other axle is a driven shaft; and only the driven shaft has the steering function. According to this, only the driven shaft which does not require an electric motor, a joint, or a reducer is steered, it is unnecessary to consider the limit of the deviation of the joint by the steering.